Korea Ever-Power · YVF2 Series · Ball Mill and Grinding Mill Drive Guide

When a ball mill is stopped with a full charge of grinding balls and ore, the balls settle and pack at the lowest point of the mill shell. The static friction between the balls and the mill lining, combined with the gravitational load of the settled charge, creates a very high starting torque requirement — typically 2.0 to 2.5 times the rated running torque. This starting torque must be provided without damaging the motor winding through excessive starting current.

When the YVF2 motor is driven by a VFD with torque-boost or vector control, the VFD can deliver motor starting torque of 1.5 to 2.0 times rated torque at zero speed without exceeding the rated motor current. This is achieved by the VFD increasing the motor flux (through higher V/Hz ratio at low frequency) to produce additional torque during the start sequence. The YVF2 Class H winding handles this elevated magnetic flux at low speed without insulation stress. Sensorless vector VFD control provides the most accurate starting torque control for ball mill applications.

Harder ores require the ball charge to drop from a higher angle, which means running at a higher percentage of critical speed (72 to 78% Nc for hard ore). Softer ores grind more efficiently at lower speed (62 to 68% Nc). A fixed-speed mill set for hard ore runs at excess speed (and excess energy consumption) when processing softer ore. VFD allows the operator to reduce mill speed for softer ore periods, saving 10 to 20% of mill drive energy.

Running at above-optimal speed for the ore type causes balls and liners to impact harder than necessary, accelerating wear. A 5% reduction in mill speed from the optimum for a given ore can reduce ball consumption by 8 to 12% and liner wear by 5 to 8%, extending maintenance intervals and reducing consumable costs. VFD adjustment to the optimum speed provides this wear reduction without sacrificing throughput.

Direct-on-line starting of large ball mill motors produces high current inrush (5 to 7 times rated) and high mechanical shock to the gearbox and mill shell as the motor comes up to speed. VFD starting ramps the motor from zero to operating speed over 5 to 15 seconds, eliminating current inrush and reducing the torque shock on the gearbox by 60 to 80%. This extends gearbox service life and reduces the frequency of gearbox gear tooth and bearing damage from heavy starts.

Industrial ball mills in cement, mining, and mineral processing typically run S1 continuous duty for 20 to 24 hours per day, stopping only for planned maintenance intervals (typically weekly or bi-weekly) and liner change shutdowns. The YVF2 motor must be rated for S1 continuous at the operating point — the mill running power at the chosen percentage of critical speed. The IC416 blower ensures this S1 rating is maintained at any speed from 40% to 100% of rated.

Mining applications at high altitude (many South American and African mining operations are at 2,000 to 4,500 m) require motor power derating for the reduced cooling air density. At 2,500 m altitude, air density is approximately 74% of sea level, reducing motor cooling capacity. Standard IEC derating: apply a power factor of 0.92 per 1,000 m above 1,000 m. At 3,000 m: derate by 1 − (2 × 0.08) = 0.84 of rated power. Specify a larger YVF2 frame to compensate for altitude derating, or specify the motor at the derated power as the S1 continuous rating for the installation altitude.

The Korea Ever-Power YVF2 series provides the complete inverter-duty motor specification for ball mill, rod mill, and grinding mill VFD drives from small laboratory mills at 0.75 kW through to medium-scale cement and mineral processing mills at 200 kW. The IC416 forced cooling system, Class H VFD-duty winding, sensorless vector control compatibility, PTC thermistor protection, and IEC 72-1 metric frame make the YVF2 the correct replacement for existing fixed-speed mill motors being retrofitted with VFD drive systems. The full range is in the VFD motor section. For large mill drive specifications above 200 kW or synchronous motor requirements, contact Korea Ever-Power.

Small pharmaceutical and research ball mills for API particle size reduction. YVF2 4-pole 0.75 to 3.0 kW IC416. Tight speed control ± 0.5 rpm for reproducible particle size distribution. Clean room compatible motor if required (BXG SS316L for pharmaceutical GMP area installation).

Porcelain, alumina, and ceramic raw material wet grinding mills for tile and sanitary ware production. YVF2 4-pole 5.5 to 55 kW. Wet grinding at 68 to 72% Nc. Speed control for different ceramic body formulations requiring different grinding fineness targets. IP55 for wet grinding building environment.

Ceramic pigment, titanium dioxide, and iron oxide pigment grinding for paint and ink manufacturing. YVF2 4-pole 2.2 to 22 kW. Precise speed control for particle size target. If grinding solvent-based pigments, specify YB2 Ex d IIB T4 for Zone 2 classification in solvent pigment areas.

Rod mills for coarse grinding in mineral processing circuits before ball mill secondary grinding. Similar drive requirements to ball mills: YVF2 4-pole 15 to 132 kW IC416, VFD control at 60 to 70% Nc. Rod mills typically have lower operating speed than ball mills of the same diameter due to the risk of rod tangling at high speed.